Surface modification on ammonium polyphosphate and its enhanced flame retardancy in thermoplastic polyurethane

Ammonium polyphosphate (APP) is an effective flame retardant in thermoplastic polyurethane (TPU). In order to further enhance the flame retardant efficiency of APP, it was coated with graphene oxide (GO) and melamine formaldehyde (MF) successively, by using 5 wt% end product of MF-GO@APP in TPU, the sample produced little dripping during burning and reached UL-94V-0 grade, peak smoke production rate was reduced from 0.132 m(2)/s in TPU to 0.051 m(2)/s, that was 61.4% decrease. Neat TPU burned out with little residue left, but by the help of 5 wt% MF-GO@APP, 24.4 wt% of char was left. These results were tried to be analyzed as relative higher heat conductivity of GO, in heating GO transferred more heat to APP and MF, resulting in earlier degradation of APP and MF, the decomposed product of MF and APP cross-linked together to form more compact char above substrate. MF-GO@APP acted as an integrated intumescent flame retardant.